Heat exchangers typically comprise separate flow paths for two fluids arranged in close contact to facilitate heat transfer between the fluids thereby cooling the higher temperature fluid while simultaneously heating the lower temperature fluid as they flow through the heat exchanger. In plate heat exchangers the flow paths are commonly provided by a series of metallic plates packed vertically in sequence with gaskets between the plates to seal the plates and separate the flow paths. This arrangement allows complex flow paths of long length for optimum heat transfer to be achieved.
Plate heat exchangers are commonly used for food processing where one of the fluids is a food product to be heated or cooled by heat exchange with the other fluid. To maintain quality of the food product being processed, it is important to avoid the food product being contaminated by cross-flow between the flow paths within the heat exchanger. To this end it is routine practice to check plate heat exchangers for any faults that may allow cross-flow to occur. Assembly/disassembly of plate heat exchangers is time consuming and it is desirable to be able to carry out such checks on the assembled heat exchanger so that disassembly for repair is only required when a leak is detected.
To this end, various methods have been proposed in the prior art for leak testing an assembled plate heat exchanger. However, these methods are generally not satisfactory for detecting small faults such as fatigue cracks or corrosion pinholes that can occur in the heat exchanger plates. While such faults may only allow a very small amount of cross-flow to occur, the resulting contamination of the food product is such that it must be thrown away and the heat exchanger disassembled to find and repair the fault. This is wasteful of the food product and time consuming to carry out a repair, all of which adds to cost.